The proposed experiments investigate the functional characteristics and structural substrate of the mechanisms controlling visual sensitivity, and focus on the role of retinal lateral excitatory and inhibitory connections in these processes. The following specific issues are addressed: 1) To what extent is sensitivity regulation strictly local and to what extent does it involve averaging excitation across the retina? 2) Does light adaptation really alter the extent of spatial integration of visual signals? 3) How is spatial integration controlled? 4) What are the precise mechanisms by which lateral inhibitory processes control sensitivity? 5) Is the state of the eye following bright light exposure functionally the same as under steady, weaker exposure? 6) What are the role of lateral neural connections in hue constancy?